1. Field of the Invention
The present invention relates to content recording apparatus, method, and computer program product for recording adjunct data in a recording medium. The adjunct data is data of a part of title content as program content.
2. Description of the Related Art
Conventionally, for example, as disclosed in documents of Advanced Access Content System (AACS) Recordable Video Book Revision 0.90 and Content Protection for Recordable Media (CPRM), in order to prevent illegal copy of the content recorded on a recording medium such as DVD, there is known a technique in which an encrypting process is performed on each of plural title content which are of a video or audio content of a program using title keys which are different in each of the title content, and the encrypted title content are recorded on the DVD medium.
In the conventional technique, each of the plural title keys is encrypted using a device key imparted in each playing apparatus such as a DVD recorder for duly recording and playing the content, and the encrypted title key is registered in the title key file and recorded on the DVD medium. When the title content is played, the encrypted title key registered in the title key file is decrypted using the device key of the recording and playback apparatus used for the play back, and the title content is decrypted with the decrypted title key to play the title content.
When a part of the title content is deleted in a rewritable DVD medium, the title key file is also updated. Specifically, the title key file is decrypted once, the title key file in which the title key corresponding to the title content deleted from the DVD medium is encrypted again using the device key, and the title key file is recorded on the DVD medium. Therefore, the title key corresponding to the deleted title content can previously be copied to prevent attack which illegally plays the title content deleted with the title key.
The above conventional technique is an effective technique in which the content input from the outside through a broadcast is protected and recorded on the recording medium such as the DVD medium to prevent unauthorized use of the content.
However, the conventional technique insufficiently protects the content (hereinafter referred to as “adjunct data”) newly generated by the recording and playing apparatus. The adjunct data is derived from AV content in which the content including the video data and audio data is compressed by an encoding method such as MPEG2 or H.264.
For example, the adjunct data is data, such as a thumbnail image or an audio file, which is used for a menu screen. Examples of the adjunct data also include data having image data compressed by the image compression format such as JPEG or GIF and audio data digitalized by an audio compression format such as LPCM or MP3. The adjunct data is image and audio content which is recorded on the DVD medium in the format different from the AV content. For generation of the adjunct data, for example the AV content whose copyright is protected are encrypted by the title key, one scene is extracted as an image file from the AV content, the image file is converted into image data to form a file, the image data file is recorded on the DVD medium, and the thumbnail is formed from the image data file. Therefore, the menu screen indicating a list of title content is generated.
Conventionally, the usage of the adjunct data is limited to the thumbnail image and the like, and the adjunct data is outputted as a file while resolution of the adjunct data is suppressed lower than the resolution of the AV content which becomes a generation source of the adjunct data. Therefore, the usage is limited and there have been a few very serious problems with the copyright.
However, in the case where the adjunct data is used for a background image of the menu screen, it is thought that the adjunct data is recorded on the DVD medium while formed in a plaintext. In this case, an unauthorized user possibly copies the adjunct data from the DVD medium to another recording medium such as a hard disk, or an unauthorized user possibly illegally distributes the adjunct data through the Internet beyond the range of fair uses in section 107 of the copyright law in the United States or private uses in section 30 of the copyright law in Japan. The adjunct data is a part of the AV content because the adjunct data is generated from the AV content. As a result, although the AV content is protected, the AV content is not protected when the adjunct data is distributed without protection.